Are there any requirements for aircraft bypass and/or lock pins? Do they have to be somehow certified by local or international aviation authorities?
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The steering bypass pin on modern airliners serves to isolate the nose wheel from the hydraulics so that movement of the nose wheel will not damage the hydraulic system. What the pin does is usually hold a bypass-valve open, allowing fluid in the actuator which is displaced by the movement of the nose wheel to 'bypass'.
This would be the most simple solution and most manufacturers have adopted this. Exceptions would be aircraft which have an electric nose wheel steering in which case the pin is not used, the pin being deactivated by a switch in the cockpit (ATR72).
In some older aircraft like the DC-8, the drag link (scissor-like link usually seen behind the nose-gear) has a quick disconnect. When disconnected the wheels are only fixed by the central oleo and can rotate thru 360 degrees. A bit of a pain for the push-back crew when reconnecting! On modern aircraft this can be done as well for non-normal operations like in the hangar or aircraft recovery. In normal conditions the actuators limit the angle of the nose wheel.
